In general, a hydraulic system discharges operation oil from a hydraulic pump, and the operation oil stands by at an inlet of a main control valve. A plurality of spools is provided inside the main control valve, and a plurality of actuators is connected to the outside of the main control valve. Further, pilot pressure, which is a flow rate control signal, is generated in a flow rate demanding unit, such as a joystick and a pedal, and the pilot pressure is provided to the main control valve. In the main control valve, a specific spool is opened/closed by the pilot pressure, and the operation oil is provided to an actuator connected to the corresponding spool by an opening/closing operation of the corresponding spool.
That is, the operation oil discharged from the hydraulic pump is provided to the actuator via the main control valve according to an operation of the joystick, and thus the actuator is operated.
In the meantime, the hydraulic pump receives power from an engine, and the engine combusts fuel to generate power.
Hereinafter, a hydraulic system of a construction machine adopting a mechanical hydraulic pump will be described with reference to accompanying FIG. 1.
FIG. 1 is a diagram for describing a hydraulic system for a construction machine.
A mechanical hydraulic pump 10 includes a swash plate r, and a discharged flow rate is controlled to be increased and decreased according to an inclination angle of the swash plate. The inclination angle of the swash plate is adjusted by a pump regulator 40.
Operation oil discharged from the hydraulic pump 10 is provided to a main control valve 20, and when a specific spool is operated in the main control valve 20, the aforementioned operation oil is provided to an actuator 30 connected to the corresponding spool. The actuator 30 receiving the operation oil is operated to perform a desired operation.
In the meantime, a worker generates a flow rate control signal by operating a joystick, a pedal, and the like. The flow control signal moves a specific spool in the main control valve 20 according to a flow rate control signal line pi.
That is, when the worker operates the joystick, the flow rate control signal operates the spool of the main control valve 20 to open/close the spool, and when the corresponding spool is opened, the operation oil is provided to the actuator 30, so that the actuator 30 performs a desired operation.
In the meantime, the hydraulic pump 10 receives power from an engine 100. The engine 100 is controlled under control of an engine control device 104.
Further, revolutions per minute (rpm) of the engine 100 may be set by an engine rpm controller 102 in advance, and the rpm may be changed by a command of a pump control device 50.
When the command of the rpm is input to the engine control device 104, the engine control device 104 operates an engine governor 106 to make fuel be provided to the engine 100. For example, when the command for increasing the rpm is given, the amount of injection fuel is increased, when the command for decreasing the rpm is given, the amount of injection fuel is decreased, and when a specific rpm is desired to be maintained, the amount of injection fuel is constantly maintained.
In the meantime, a gear pump 70, which is an auxiliary pump, is further provided in the hydraulic pump 10. The gear pump 70 provides pilot operation oil to the joystick, the pedal, and the like, and generates a flow rate control signal when the worker operates the joystick and the pedal to transmit a pressure of the flow rate control signal.
In the meantime, a first hydraulic line L1 is connected so that the pilot operation oil discharged from the gear pump 70 passes through an electronic proportional pressure reducing valve 60 to be connected to a shuttle valve 80. One side of the shuttle valve 80 receives a flow rate control signal pi. The shuttle valve 80 selects a larger pressure between a pressure of the first hydraulic line L1 and the pressure of the flow rate control signal line, and provides the selected pressure to a pump regulator 40 through a second hydraulic line L2.
The aforementioned electronic proportional pressure reducing valve 60 receives a control signal from the aforementioned pump control device 50 through a first signal line s1. Particularly, when an optional operation (ex. a breaker/shear) is performed in the construction machine, a higher pressure is output by comparing the pilot pressure of the flow rate control signal line pi with a pressure corresponding to a flow rate set for the optional operation by using the electronic proportional pressure reducing valve 60 to control the flow rate.
Hereinafter, the pump regulator 40 for controlling the hydraulic pump 10 will be described with reference to FIGS. 1 and 2.
FIG. 2 is a diagram for describing a control of the mechanical hydraulic pump in the hydraulic system of the construction machine.
The control of the mechanical hydraulic pump 10 includes a flow control, a constant horse power control, and a power shift control, and will be described in detail based on each control.
[Flow Control]
The flow control generates a demanded flow rate by operating the joystick, and the flow rate control signal pi corresponding to displacement of an operation of the joystick is generated by the flow control. For example, when the flow rate control signal pi is increased from p1 to p2 as illustrated in FIG. 2A, the pump regulator 40 controls a flow rate Qp to be increased from q1 to q2 by adjusting the swash plate r. Accordingly, a discharged flow rate of the hydraulic pump 10 is increased.
[Constant Horse Power Control]
The constant Horse power control controls a constant pump horse power, which is set by receiving a load pressure Pd, to be maintained.
In the constant horse power control, a correlation between the pressure and the flow rate is set as a P-Q map, and the discharged flow rate is changed according to the P-Q map set by receiving the pressure load Pd applied to a hydraulic line between the hydraulic pump 10 and the main control valve 20.
For example, when the load pressure Pd is increased from p1 to p2 as illustrated in FIG. 2B, the pump regulator 40 controls the flow rate Qp to be decreased from q1 to q2 by adjusting the swash plate r. Accordingly, the discharged flow rate of the hydraulic pump 10 is controlled to be decreased, but the pump horse power is constantly maintained.
[Power Shift Control]
The power shift control is a control of adjusting a pump horse power according to a load state of the engine. That is, a plurality of P-Q maps is set in the constant horse power control, and a P-Q map is selected from the plurality of P-Q maps according to a load to control the hydraulic pump. The plurality of P-Q maps receives a command from the pump control device 50 through a second signal line s2.
For example, as illustrated in FIG. 2C, the plurality of P-Q maps may be provided as a heavy load map, a standard load map, and a light load map, and the hydraulic pump is controlled by selecting a specific P-Q map according to a load.
Accordingly, even though the same load pressure Pd is applied, when the heavy load map is selected, a large flow rate corresponding to q1 is discharged. However, when the standard load map is selected, a flow rate corresponding to q2, which is smaller than q1, is discharged. Further, when the light load map is selected, a flow rate corresponding to q3, which is smaller than q2, is discharged.
That is, according to the power shift control, when it is determined that a load of an operation target is large, the P-Q map close to a heavy load is selected, when it is determined that the load of the operation target is general, the standard load map is selected, and when it is determined that the load of the operation target is small, the P-Q map close to a light load is selected, thereby controlling the hydraulic pump 10.
The hydraulic system in the related art, which is configured and operated as described above has problems below.
When the joystick is suddenly operated, so that a large flow rate is suddenly and instantaneously demanded, the hydraulic system becomes temporarily unstable, which will be described with reference to FIGS. 3 and 4.
FIG. 3 is a diagram for describing a change in a flow rate in the constant horse power control in the hydraulic system of the construction machine in the related art. FIG. 4 is a diagram for describing a change in a pump discharged flow rate, a change in an rpm of an engine, and a change in an output of the engine by an operation of the joystick in the hydraulic system of the construction machine in the related art.
As illustrated in FIG. 3, when the pump load pressure Pd is suddenly increased, the flow rate is suddenly increased so as to respond to the sudden increase of the load pressure Pd. However, a capacity of the hydraulic pump 10 is physically limited, so that there is a case where when an excessive flow rate is demanded, the demanded flow rate exceeds a range handled by the hydraulic pump 10, and in this case, the flow rate is controlled to be gradually decreased by the constant horse power control.
That is, the pump load pressure is maintained at the low pressure p1 at an initial stage and the small flow rate q1 is discharged, and when the demanded flow rate is suddenly increased, the flow rate Qp is suddenly increased in comparison with a change in the pump load pressure Pd, so that the flow rate Qp is increased to a maximum flow rate q2, and then, the flow rate is controlled to be decreased by the constant horse power control and thus the decreased flow rate Qp is discharged. Then, the flow rate is stabilized from a stabilization time point t2 while maintaining the high pump load pressure Pd.
As described above, when the joystick is suddenly operated, as illustrated in FIG. 4A, as can be seen from the change in the pump discharged flow rate, a delta flow rate delta Qp is discharged until just before a maximum flow rate immediately after a joystick operation time point t1, and the flow rate is stabilized by the constant horse power control after a predetermined time elapses.
As described above, the excessive operation oil flow rate, which is discharged from a peak portion indicated by the delta flow rate Qp to the stabilization of the hydraulic pump due to the sudden increase in the flow rate generates a hydraulic impact, thereby making the hydraulic system be unstable.
Further, as illustrated in FIG. 4B, investigating a change in the rpm of the engine, large power is instantaneously demanded, but the rpm of the engine is not immediately reflected due to a mechanical dynamic property, and the rpm of the engine is sharply decreased, so that a delta rpm is also decreased. Then, after a speed of a turbo charger is increased and fuel is appropriately injected, the rpm of the engine reaches a target rpm.
That is, in the hydraulic system using the mechanical hydraulic pump 10 in the related art, there is a problem in that when the demanded flow rate is sharply increased, the rpm of the engine is sharply decreased or the engine is stalled.
Further, even when the engine is stalled or the rpm of the engine is sharply decreased as described above, fuel is continuously supplied, thereby degrading fuel efficiency.
The decrease phenomenon of the rpm of the engine will be additionally described with reference to FIG. 4C.
When the demanded flow rate is increased, the hydraulic pump 10 requires larger power, so that the rpm of the engine 100 is increased. However, it is impossible to immediately implement a desired rpm due to the mechanical dynamic property. The reason is that an engine governing section is required until the rpm of the engine is increased. Particularly, a turbo charger time lack section is present in the engine governing section because a predetermined time is inevitably consumed until the turbo charger is rotated from a low speed to a high speed. Accordingly, when the demanded flow rate is suddenly increased, the rpm of the engine is increased within an allowed range of the output of the engine, and is delayed until the turbo charger is normally operated, and the rpm of the engine is increased when the turbo charger normally performs the function.
In the meantime, in a construction machine including the mechanical hydraulic pump in the related art, a rotation speed of the engine is decreased by a hydraulic load when an initial operation is performed, and a controller detects the decrease in the rotation speed of the engine to decrease a pump load through a power shift control (pump power shift control) so as to prevent the rotation speed of the engine from being decreased.
However, the power shift control does not have a method of decreasing a flow rate control of determining a flow rate discharged by a joystick lever or a driving lever, so that there is a problem in that when an initial operation or a sudden operation is performed, the rpm of the engine is decreased.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.